1. Field of the Invention
The invention is directed to a method, to a mobile station and to a base station for signal transmission via a radio interface between radio stations of a time division multiple access (TDMA) mobile communication system.
2. Description of the Related Art
Mobile communication systems serve for the transmission of data with the assistance of electromagnetic waves via a radio interface between a transmitting and a receiving radio station, in which one of the radio stations is usually not stationary. The known GSM mobile radio telephone network (Global System for Mobile Communications) is an example of a mobile communication system, in which a channel respectively formed by a narrow band frequency range and a time slot is provided for the transmission of a subscriber signal. Since a subscriber signal in a channel is separated from other subscriber signals in frequency and time, the receiving radio station can undertake a detection of the data of this subscriber signal. Due to the formation of time slots, a time-division multiplex subscriber separation and, thus, a TDMA (time division multiple access) mobile communication system is present.
The network-side radio station of a mobile radio telephone network is a base station that communicates with mobile stations via a radio interface. The transmission from a mobile station to the base station is referred to as the upstream direction and the transmission from the base station to a mobile station is referred to as the downstream direction. A channel is formed by at least one time slot per time-division multiplex frame. A plurality of time-division multiplex frames thereby form a macro frame. Furthermore, the carrier frequency and, potentially, a frequency discontinuity sequence identify the channel.
Connection-oriented concepts and concepts on the basis of logical connections can be accessed for the transmission of data between two communication terminal devices. For connection-oriented data transmissions, physical resources between the two communication terminal equipment must be offered during the entire time of the data transmission.
A permanent offering of physical resources is not necessary for a data transmission via logical connections. One example of such a data transmission is packet data transmission. A logical connection between the two communication terminal devices is present for packet data transmission over the duration of the entire data transmission; however, physical resources are only offered during the actual transmission times of the data packets. This method is based on this principle in that the data are communicated in short data packets between which longer pauses can occur. The physical resources are available for other logical connections in the pauses between the data packets. Physical resources are thus saved when utilizing such a logical connection.
The packet data transmission method disclosed by German Letters Patent DE 44 02 903 A1 is particularly available for communication systems having limited physical resources. For example, in mobile radio telephone systems such as the GSM mobile radio telephone system, the physical resources of the radio interface, i.e., the radio-oriented resources, in the frequency domainxe2x80x94the number of frequency bands and time slotsxe2x80x94are limited and must be rationally utilized.
When a data transmission from a mobile station in a waiting condition to the network is desired, i.e., in the upstream direction, this mobile station will express an access request that is interpreted by the network. To accomplish this, channels in which signaling messages required for an arbitrary access that could not be previously planned but in which no payload data are transmitted, are provided within the packet data channel for access.
The access request is expressed by what is referred to as an access burst (random access burst) that is shortened in comparison to normal radio bursts so that a reception can also proceed without time synchronization of the radio stations. This access burst is always abbreviated. Regardless of the condition of the mobile station no precautions are taken for influencing the transmission point in time for the access burst. Each mobile station arbitrarily selects this transmission point in time within the time slot.
The invention is based on the object of specifying an improved method and improved devices for signal transmission of a TDMA mobile communication system that more effectively use the radio-oriented resources of the radio interface.
This object is achieved by transmitting a first radio burst in a time slot, performing a transmission-side synchronization of this transmission so that this burst arrives at a receiver at a predetermined point in time within the time slot, and transmitting a second radio burst in the same time slot in a manner where the second burst can be evaluated separately from the first burst.
This object can also be achieved by transmitting a first radio burst that is shorter with respect to other radio bursts as an access burst in a time slot, and performing a transmission-side synchronization of the transmission.
Furthermore, a mobile station may be used which has a transmitter/receiver for transmitting and receiving radio bursts, a signal processor for generating a first radio burst or a second radio burst, a controller for synchronizing the transmission of the first radio burst within a time slot and for triggering the transmission of the first radio burst. This mobile station may be used with further mobile stations for sending a second radio burst(s), and a base station that interprets the second radio burst separately from the first radio burst within the same time slot, in which the controller synchronization leads to a predetermined reception point in time within the time slot at the base station.
Finally, the object of the invention may also be realized using a base station having a receiver for receiving two time-separable radio bursts sent in a time slot from different mobile stations and a signal evaluator for separating and processing these radio bursts. Advantageous developments of the invention can be derived from the discussion below.
In methods for signal transmission, a first radio burst is inventively transmitted in a time slot of the radio interface, in which a transmission-side synchronization of the transmission of the first radio burst takes place, so that the first radio burst arrives at the receiving radio station at a predetermined point in time within the time slot. At least one second radio burst that can be evaluated separately from the first radio burst is transmitted in the same time slot. A corresponding subdivision of a time slot creates the possibility of transmitting a greater quantity of data and, thus, of using the radio-oriented resources more effectively. A time slot is thus allocated to not only one mobile station but can be used by a plurality of mobile stations independently of one another. Due to the transmission-side synchronization, it can be assured that the radio bursts do not arrive simultaneously in the time slot and can thus be separately evaluated. Not all time slots of the TDMA radio communication system are fashioned in this way; rather, the subdivision into two separate radio bursts that could derive from different transmitters or that may be intended for different receivers is enabled only for individual time slots within a frame.
According to a development of the invention, the radio bursts transmitted in a time slot have the same length. A plurality of standardized block lengths is thus introduced which fill up a time slot such that optimally few unused transmission times arise and a time slot is filled with two, three or more radio bursts as needed. A great number of very short messages can thus be transmitted. This method can be relevantly applied in mobile radio telephone systems of the third generation such as, universal mobile telecommunications services (UMTS).
Alternatively, when different types of radio bursts are transmitted in a time slot, then mixed payload and signaling information can also be transmitted in a time slot. Existing standardized radio bursts need not be adapted, yet additional radio bursts can be transmitted in the remaining time of the time slot. A very flexible radio interface thus arises that can offer new services with the additional, second radio bursts, without having to make further radio-oriented resources available.
The inventive method encounters an especially advantageous application for radio stations that are formed by base stations and mobile stations, in which the first radio burst is an abbreviated radio burst compared to other radio bursts. Poor utilization of the radio-oriented resources of the radio interface exist, particularly for abbreviated radio bursts, this situation has not been improved since the detectability of the radio bursts dominated.
When the mobile communication system is a GSMA mobile radio telephone network and the first radio burst is what is referred to as an access radio burst, then only approximately half of a time slot is filled and the unutilized portion can be exploited by the inventive method.
The invention can also be described by a method for signal transmission via a radio interface between mobile stations and a base station of a TDMA mobile communication system. In this method, a first, abbreviated radio burst is transmitted in the upstream direction as an access burst in a time slot of the radio interface, following a transmission-side synchronization, and arriving at the receiving radio station at a predetermined point in time within the time slot.
The access bursts are significantly shorter than the time slots and have previously not been synchronized since one wished to accord the mobile stations fast access at any time even in the non-synchronized condition. What this fails to recognize, however, is that given a packet data transmission, for example, the mobile stations are already synchronized in the standby condition. The point in time of the arrival of an access burst at the base station is thus also predictable, and the remaining time of a time slot can be used in some other way, for example, for measuring the channel using the base station, for lengthening the access burst, for shutting the receiver off or for transmission of a second radio burst.
The transmission of the radio bursts is advantageously synchronized such that the points in time of the arrival of the radio bursts need two radio bursts that essentially do not overlap. A significantly simpler distortion correction and decoding is thus possible. Minute overlaps caused by multipath propagation can, however, be tolerated.
Advantageously, the point in time of the arrival of the first radio burst is oriented to the start of the time slot. The values of time compensation, the timing advance, that have already been determined can thus be accepted and additional calculating effort is not necessary.